It is known that it is relatively difficult to achieve a uniform winding density in a wound roll which is formed from very thin foils or films. The winding density depends upon air inclusions between the successive turns or layers and upon the web speed and the surface roughness of the web.
An additional problem is that webs of different types have properties which themselves introduce variations in the winding density. One characteristic that plays a prominent roll in this respect is the fact that the properties of the web may differ physically in different directions
During the winding of a roll, therefore, a variety of defects can result. These include so-called telescoping, fold formation, nonround coils and the like. Some of these defects may be discoverable only after substantial standing of the rolls.
To overcome these drawbacks, conventional rotary turret or reel-type multiple-station coils have used systems intended to avoid these drawbacks. However, in almost all cases, the contact roller must be brought out of engagement with the roll being wound for at least a brief period sufficient to cause loosening or unwinding of the final turn.
It has been proposed, to overcome this disadvantage, to provide auxiliary contact rolls which can be mounted in a rotary turret or the like or can be provided externally in a so-called follower system. Such systems are rather expensive to construct so that such contact devices with two different contact systems are not widely used and have not been found to be satisfactory heretofore since the use of the system results in a defect in the winding process.